Cockpit lighting demands for military or other professional aircraft may be impacted by nighttime, or other low light, operations. In particular, at times during operation of the aircraft, flight crews may have donned night vision goggles or similar equipment to enhance visibility of terrain and other features outside the aircraft. Because these goggles are sensitive to infrared and near-infrared radiation, cockpit illumination often must be designed to minimize output in these regions of the lighting spectrum. Illumination of this type that meets military or other recognized standards in this area is frequently referred to as “NVIS compliant.”
U.S. Pat. No. 6,786,617 to Lemay, et al., whose contents are incorporated herein in their entirety by this reference, discusses use of light-emitting diodes (LEDs) for these purposes. Although LEDs are advantageous over incandescent lighting in many ways, visible-wavelength LEDs can also emit energy in the infrared and near-infrared portions of the spectrum and thus must have their light filtered for use with NVIS equipment. Accordingly, the Lemay patent describes an assembly of green and blue LEDs whose light is filtered to be NVIS compliant. See Lemay, col. 2, 11. 47-58. As detailed in the Lemay patent:                It is another object of this invention to provide an electronic component for use in a night vision imaging system environment comprising a printed circuit board assembly comprising a light source having an emission non-compliant to the night vision imaging system standard, a conformal coating covering the printed circuit board assembly, including an absorbing agent, for filtering quantities of energy of the emission, such that the infrared emission of the printed circuit board assembly is filtered by the absorbing agent.Id., col. 3, ll. 1-9.        
Illustrated in FIG. 2 of the Lemay patent is “a typical assembly of light emitting diodes producing light compliant with a night vision imaging system standard.” Id., ll. 28-30. Shown in the figure are two LEDs (green and blue) assembled on a printed circuit board and coated externally with a conformal coating to which absorbing dye has been added. An optical filter and diffusing film may also be positioned atop the LEDs, with the conformal coating instead applied to the diffusing film in an alternative version of the assembly. See id., col. 5, ll. 7-48. Absent inclusion of (at least) the external conformal coating with its absorbing dye, the assembly would not be NVIS compliant.
FIG. 1 of this application depicts a conventional system similar to that of the Lemay patent. As shown in FIG. 1, a standard surface-mount LED package 10 includes an encapsulated LED die 14 positioned within a housing 18, with the encapsulant 22 typically comprising phosphor 26. An external filtering dye or pigment 30 (which may be in the form of a doped glass or polymeric film) is then coated onto or bonded to the exterior of the housing 18. In yet other existing systems, the filtering material is separated from—but still external to—the housing of the LED.
Unaddressed by these or any other existing NVIS-compliant systems known to applicant is the concept of providing filtering material internal to an LED package. Such concept avoids any necessity of coating or bonding external filters to the package, reducing manufacturing time and expense. It also reduces the possibility of the external filtering material abrading or otherwise wearing in use.